Nanocomposites are polymer systems containing inorganic particles with at least one dimension in the nanometer range. Some examples of these are disclosed in U.S. Pat. Nos. 6,060,549, 6,103,817, 6,034,164, 5,973,053, 5,936,023, 5,883,173, 5,807,629, 5,665,183, 5,576,373, and 5,576,372. Common types of inorganic particles used in nanocomposites are phyllosilicates, an inorganic substance from the general class of so called “nano-clays” or “clays.” Ideally, intercalation should take place in the nanocomposite, wherein the polymer inserts into the space or gallery between the clay surfaces. Ultimately, it is desirable to have exfoliation, wherein the polymer is fully dispersed with the individual nanometer-size clay platelets. Due to the general enhancement in air barrier qualities of various polymer blends when clays are present, there is a desire for a nanocomposite with low air permeability; especially a vulcanized elastomer nanocomposite such as used in the manufacture of tires.
The preparation of nanocomposites uses a number of methods to generate exfoliated clays. One of the most common methods relies upon the use of organically modified montmorillonite clays. Organoclays are typically produced through solution based ion-exchange reactions that replace sodium ions that exist on the surface of sodium montmorillonite with organic molecules such as alkyl or aryl ammonium compounds and typically known in the industry as swelling or exfoliating agents. See, e.g., U.S. Pat. No. 5,807,629, WO 02/100935, and WO 02/100936. Other background references include U.S. Pat. Nos. 5,576,373, 5,665,183, 5,807,629, 5,936,023, 6,121,361, WO 94/22680, WO 01/85831, and WO 04/058874.
Elastomeric nanocomposite innerliners and innertubes have been formed using a complexing agent and a rubber, where the agent is a reactive rubber having positively charged groups and a layered silicate uniformly dispersed therein. See, for example, Kresge et al. U.S. Pat. Nos. 5,665,183 and 5,576,373. This approach uses pre-formed positively charged reactive rubber components.
Nanocomposites have also been formed using non-ionic, brominated copolymers of isobutylene and para-methylstyrene, and blends of these copolymers with other polymers. See, for example, Elspass et al., U.S. Pat. Nos. 5,807,629, and 6,034,164. Star-branched polymers were disclosed as secondary blend polymers with brominated copolymers of isobutylene and para-methylstyrene in commonly assigned aforementioned WO 02/100935 and WO 02/100936 to Dias et al.
Although the above disclosed nanocomposites have resulted in nanocomposites having good barrier properties, there still exists a need to develop nanocomposites having minimal permeability which can be prepared from elastomers having good processability properties such as green strength and relaxation characteristics.